Combination slip ring and terminal for variable resistance device



y 1968 J. P. DOERING, JR 3,382,474

COMBINATION SLIP RING AND TERMINAL FOR VARIABLE RESISTANCE DEVICE Filed June 27. 1966 INVENTOR.

JOHN P; DOERING JR.

BY WWW ATTORNEY United States Patent 3,382,474 COMBINATION SLIP RING AND TERMINAL FOR VARIABLE RESISTANCE DEVICE John P. Doering, In, Santa Ana, Calif., assignor to Beckman Instruments, Inc., a corporation of California Filed June 27, 1966, Ser. No. 560,576 3 Claims. (Cl. 338-174) ABSTRACT OF THE DISCLOSURE A slip ring and terminal structure for a variable resistance device comprising a substantially closed ring of wire or other resilient electrically conductive material having one end thereof bent outwardly into a terminal extension which protrudes outwardly through an opening formed in the side wall of the housing of the device. The ring is supported on the inner surface of the cavity within the housing adjacent the resistance element and is contacted by an electrically conductive wiper as it traverses its rotational path around the resistance element mounted within the housing.

The present invention relates to variable electrical resistance devices such as potentiometers, rheostats, and the like, and, is more particularly directed to a slip ring and terminal member arrangement for such devices.

The most common type of slip ring in a potentiometer or variable resistance device is usually attached to and rotates with the hub or shaft of the potentiometer which drives the wiper or movable electrical contact engaging the resistance element. Electrical connection to the outside of the potentiometer is usually made by means of slip ring wipers which are attached to a terminal and are slidingly engaged with the slip ring on the hub or shaft. The reverse of the above arrangement is also used. That is, the slip ring may be a stationary ring or disc mounted on the potentiometer lid or other surface concentric with the axis of the shaft and brushes or wires are rotated with the shaft and wipe against the face of the slip ring disc to carry current to the rotating wipers. Both of these arrangements are somewhat expensive and the latter arrangement is not generally suitable for multisection, single-turn potentiometers or variable resistance devices. Both arrangements require separate terminal connections and assembly thereof in order to attach the slip ring or the brush means into an external circuitry.

The advantages of the present invention will become apparent as the following description proceeds and the features of novelty which characterize the invention will be pointed out with particularity in the claims annexed to and forming a part of the specification.

Briefly, the present invention is directed to a variable potentiometer or resistance device having a housing with side walls defining a cavity in which is mounted an annular resistance element and a slip ring both being concentrically arranged about a common axis. The slip ring is a resilient member of wire or other resilient electrically inductive material formed into the shape of a substantially closed ring with one end thereof bent outwardly into a terminal extension which protrudes outwardly from the ring through an opening in the side wall of the case thereby providing an integrally attached terminal for connecting the slip ring into an external electrical circuit. An electrically conductive wiper contacts the exposed surfaces respectively of the annular resistance element and slip ring during excursion of the wiper around its rotational path and conducts an electrical current flow between these two members.

For a better understanding of the invention, reference may be had to the accompanying drawing in which:

FIGURE 1 is a perspective view of the spring wire slip ring forming the preferred embodiment of the present invention;

FIGURE 2 is a front elevation view of the slip ring;

FIGURE 3 is an enlarged partial cross-sectional view of the slip ring mounted within a housing and illustrating the wiper adapted to traverse the slip ring and resistance element; and

FIGURE 4 is an enlarged partial cross-sectional view showing the mounting arrangement of the slip ring with a looped end extending through the opening in the housing to form an electrical terminal.

Referring now to the drawing, in FIGURE 1 there is shown a new and improved slip ring of the present invention which is formed of a conductive wire (generally designated by the reference numeral 10) formed into a circular shape or ring 11. Preferably the wire is formed of a material, which is resilient or capable of exerting spring force when shaped, and is preferably formed into a single helical turn with the end portions 12 and 13 overlapping each other to some extent. One end of the ring is bent outwardly to form a terminal extension 14 which, in the embodiment shown in FIGURE 1, is a reverse bend and forms a loop lying substantially in the plane of the ring. While the terminal extension 14, in the illustrated embodiment is in the shape of a loop, it could also take the form of a post or post with a small eyelet or any other advantageous shape which could extend through the housing as will be later described. The wire 10 is best selected of some material which is resistant to corrosion and wear, such as a brass wire spring, which has been hard gold plated.

While not believed essential to the proper operation and assembly of the ring, it has been found advantageous in the preferred embodiment to bend the tip of the wire opposite from the end forming the terminal extension or loop 14 outwardly laterally with respect to the plane of the ring. That is, the opposite end 12 is formed so that a small tip portion 17 is bent outwardly substantially normal to the plane of the ring 11. As will be explained, the tip portion 17 aids in supporting the ring and terminal assembly within a potentiometer housing.

Referring now to FIGURE 3, the slip ring 11 is shown mounted within a housing 16 including a side wall or walls 15 defining a cavity 18 within which is also mounted an annular resistance element 19. In the illustrated embodiment, the side wall 15 forms a cylindrical shaped housing and the resistance element is disposed around the periphery of the cylindrical cavity 18 formed therein. The housing is preferably formed of an insulating material and may be molded from a plastic material, such as diallyl phthlate. As shown in FIGURE 3, the resistance element 19 comprises a fine resistance wire 20 which is helically wound upon an annular mandrel 21. In the illustrated embodiment, the housing is provided with a shoulder or abutment 22 extending radially inwardly from the surface of the cavity. The resistance element 19 and the slip ring 11 are disposed or mounted on opposite sides of the shoulder 22 within the cavity 18 and the shoulder 22 serves as a mounting and locating means during the assembly of these components.

As may best be seen in FIGURE 3, a shaft 25 is rotatably mounted within the housing. The shaft 25, in the illustrated embodiment, extends through the end cover 26 and is accessible from this end of the variable resistance device. A rotor, generally indicated by the reference numeral 27, is attached to the shaft and carries an electrically conductive wiper or contact member 28, which rotates with the shaft and rotor. In the illustrated embodiment, the wiper 28 is bifurcated to form a pair of contact arms 29 and 30. The wiper arms 29 and 30 are preferably spring biased into contact with the inner surfaces of the slip ring 11 and the resistance element 19.

During rotational excursion of the wiper member, the

bifurcated wiper 19 conducts electrical current between the slip ring 11 and the resistance element 19 at successive points along the path of rotation of the wiper.

As will be noted in FIGURE 3, the contact surface of the wiper contact arm 29, which engages the slip ring 11, is made sufficiently wide so that it maintains continuous contact with the slip ring even though successive points on the slip ring are not in precisely the same plane. As will be seen in FIGURE 2, in the preferred embodiment, which is illustrated, the slip ring is in the form of a helical turn so that the inner surfaces of the successive points along the ring are not in precisely the same plane with respect to the rotational path of the wiper. By making the plane of the slip ring 11 slightly dilferent from the plane of the rotational path transcribed by the wiper arm 29 the life of the wiper contact 20 is increased by distributing the wear across the entire surface 29a of the contact arm 29. This same objective can be accomplished using a slip ring which is substantially circular in shape, by mounting the ring so that its plane is slightly at an angle with respect to the plane of the Wiper arm 29.

Referring now to FIGURE 4, it will be seen that the housing 16 is provided with an opening 31 extending therethrough and communicating with the cavity 18. The terminal extension or loop 14, formed on the end of the spring wire 10, is inserted through the opening 31 during assembly and extends outwardly from the housing to form a terminal for connecting the slip ring into an electrical circuit. In practice, the outer circumference of the ring 11 is greater than the inner circumference of the cavity 18 so that it is necessary to compress the ring during assembly. Upon expansion within the cavity 18 with the terminal extension or loop 14 through the hole 31 the ring is securely held in place.

A further device for retaining the slip ring, as shown in FIGURE 4, includes a small hole 32 formed laterally within the shoulder 22, which serves as a recess to receive the tip 17 formed on the end of the spring wire 10. The holes 32 and 31 and the terminal extension 14 and tip 17 serve to lock the slip ring and terminal member firmly within the housing and prevent disengagement therefrom. The tip 17 which is formed at an angle to the slip ring serves to anchor one end of the slip ring and, since the end sections 12 and 13 of the slip ring overlap slightly (see FIGURE 1), the tip 17 is retained in the hole 32 by the terminal extension 14 of the slip ring as it extends through the hole 31 of the side wall of the housing.

For electrically connecting the resistance element into an electrical circuitry, there is provided at least one terminal member 36 extending outwardly from the side wall 17 of the housing and firmly supported thereon. Means are provided for connecting the terminal member 36 t the resistance element 19, such as lead wires 37 tap welded to the resistance wire and to the terminal member respectively. Terminal member 36 may be formed and mounted in accordance with the arrangements disclosed in copendiug patent application Ser. No. 557,540 filed in the name of John Doering, Jr., entitled Resistance Device and Terminal Therefor and assigned to Beckman Instruments, Inc., the assignee of the present invention. In such an arrangement, the terminal 36 is mounted within a pair of slots 38 and 40 formed in the side Wall 17 of the housing and retained therein by an abutting shoulder 39 extending from the cover lid 26, which retains the terminal 36 securely in place within the housing.

While the slip ring and terminal member 11 is securely retained in place by means of the end tip 17 and the extension or loop 14, it may be desirable to further secure the ring in place by means of a retaining means holding the ring 11 against the shoulder 22 of the housing. As may be seen in FIGURES 3 and 4, a plurality of bosses or lugs 41 extend outwardly from the inner surface of the cavity and serve to form a mounting seat between the bosses and the shoulder 22 for receiving the slip ring 11. Bosses 41 may be arranged or molded in the housing during the formation thereof and their particular location depends primarily upon the shape of the slip ring 11. In the illustrated embodiment, the bosses are arranged to receive the helical shape of the slip ring 11 and force the bottom portion into abutting relationship against the shoulder 22. The circumferential distance around the upper surface of the lugs 41 is made smaller than the outer circumference of the spring wire slip ring so that the slip ring must be compressed when inserted into the space between the lugs and the annular shoulder 22. Thus, during assembly, the slip ring 11 which is of spring or resilient material is compressed to decrease the outer circumference thereof and permit it to slide over the surface of the lugs 41. The ring is then released to expand it into position within the space provided for the slip ring 11 adjacent the shoulder 22 of the housing. While the lugs are not absolutely essential for retaining the slip ring in place within the cavity, they do aid in retaining it and are easily molded along with the housing.

It will be understood that the opening 31 need not be a hole directly through the side wall 17 of the housing. It may also comprise a slot, similar to slot 38 in which terminal 36 is inserted. The slot is open on one side and may be substantially closed and the terminal extension or loop 14 captured therein by the rear lid or an abutment protruding from the rear lid when the lid is positioned on the potentiometer housing.

While in accordance with the patent statutes there 7,

has been shown and described what at present is considered to be the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, the intent of the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. A variable resistance device comprising:

a housing including side walls defining an annular cavity, said housing having an opening through a side wall thereof communicating with said cavity, said housing having an annular shoulder protruding inwardly around the inner surface of said housing into said cavity, said annular shoulder having a hole therein opening on at least one side thereof into said cavity;

an annular resistance element mounted in said housing around the inner periphery of said cavity;

terminal means electrically connecting with said resistance element for connecting said element into an electrical circuit;

a slip ring and terminal member disposed in said housing comprising a resilient wire member of electrically conductive material formed into a substantially closed slip ring, said ring being supported by the side walls defining said cavity and positioned adjacent said annular shoulder protruding into said cavity, said slip ring having a surface thereon arranged concentrically with respect to the axis passing through said annular resistance element,

one end of said resilient wire being bent outwardly to form a terminal extension protruding outwardly substantially in the plane of said ring, said terminal extension extending through said opening in said housing for connection into an electrical circuit,

said ring having its end thereof opposite from said end forming said outwardly extending loop bent at an angle and seated in said hole in said annular shoulder thereby retaining the upper portion of said slip ring between said hole in said annular shoulder and said loop protruding through said hole in said side walls of said housing; and

an electrically conductive wiper member mounted for rotational movement within said cavity, said wiper during its rotational excursion electrically contacting and conducting electrical current between said resistance element and said slip ring.

2. The variable resistance device defined in claim 1 in which said spring wire is formed into a helical turn with opposite ends thereof partially overlapping for a short extent of said turn.

3. A variable resistance device comprising:

a housing including side walls defining an annular cavity, said housing having an opening through a side wall thereof communicating with said cavity, an annular shoulder protruding inwardly around the inner surface of said housing into said cavity;

an annular resistance element mounted in said housing around the inner peripheral surface of said cavity;

terminal means electrically connecting with said resistance element for connecting said element into an electrical circuit;

a slip ring and terminal member disposed in said housing comprising a resilient wire member of electrically conductive material formed into a slip ring having the shape of a closed helical turn with opposite ends thereof partially overlapping for a short extent of said turn, said slip ring being supported by the side walls defining said cavity and positioned concentrically with respect to the axis passing through said annular resistance element,

one end of said resilient spring wire being bent outwardly to form a terminal extension protruding outwardly substantially in the plane of said slip ring, said terminal extension extending through said opening in said housing for connection into an electrical circuit,

a plurality of protruding bosses extending from the inner surface of said side wall of said housing and spaced from said inner annular shoulder a distance sufiicient to receive said spring wire slip ring and retain said ring in place against said shoulder, the circumferential distance around the projected upper surfaces of said lugs being smaller than the outer circumference of said slip ring so that said slip ring must be compressed when inserted into the space between said lugs and said annular shoulder and when said slip ring is expanded in said space it is securely retained in the space between said lugs and said annular shoulder; and

an electrically conductive wiper member mounted for rotational movement within said cavity, said wiper during its rotational excursion electrically contact ing and conducting electrical current between said resistance element and said spring wire slip ring.

References Cited UNITED STATES PATENTS 2,489,757 11/1949 Dressel 338--174 X 2,815,422 12/1957 Lock 338-146 ROBERT K. SCHAEFER, Primary Examiner. H. HOHAUSER, Assistant Examiner. 

